High-frequency modulator apparatus



Jan. 8, 1952 E. L. GlNzToN HIGH-FREQUENCY MODULATOR APPARATUS original Filed Jan. 29, 1942 OUTPT FREQUENCY a. fl. E our/20T /A/ TEA/sf TY REFL Ec To R PL A TE VOL TAGE INVENTOR. [0W/4R0 G//Vzo/V Patented Jan 8, 1952 UNITED STATESv PATENT OFFICE HIGH-FREQUENCY MODULATOR APPARATUS Edward L. Ginzton, Redwood, Calif., assignor to The Sperry Corporation, a

Waffe corporation of Dela- Original application January 29, 1942, Serial No./

428,682, now Patent No.

nary 21, 1947.

2,414,785, dated Jan- Divided and this application December 14, 1946, Serial No. 716,212

- 11 Claims. l

The present invention relates generally to microwave electron discharge apparatus and circuits therefor and more specifically to modulators at microwave frequencies. The present application is a division of application Serial No. 428,682 for High Frequency Tube Structure," led Januax-y 29, 1942, and which issued as U. S. Patent No. 2,414,785, dated January 21, 1947.

In Fig. 2 of Patent No. 2,250,511, for Stabilization of Frequency, granted June 17, 1941, to Russell H. Varian, there is disclosed an electron rial No. 428,682.

discharge device which has come to be known by the name Reflex Klystron. This device includes a cavity resonator having a pair of electron-permeable grids or electrodes defining a gap across which an electron stream is projected to become velocity-modulated by the action of the alternating electric field across the gap. The velocity-modulated electrons are thereafter reversed in flight by a reflector electrode in their path and are returned into 'the resonator gap, where, upon suitable adjustment of the parameters of the system, these electrons yield up ultrahigh-frequency energy to the field within the resonator, whereby sustained oscillations are proyduced suitable for general use in any utilization device to which the resonator may be coupled. Thus, the electron stream undergoes regularly- `'recurrent velocity changes and, subsequent thereto, is formed into regularly-recurrent bunches. The recurrence of the velocity changes and the bunching is systematic and varies uniformly with time.

yAccording to the present invention, simple means are provided for producing modulation of the output derived from such a cavity resonator in accordance with intelligence signals by impressing such intelligence signals upon the reector electrode.

, Accordingly, it is a primary object of the present invention to provide improved modulated electron discharge apparatus.

It is a further object of the present invention to provide relatively simple circuits for producing modulation of microwave oscillations generated by reilex klystrons.

Other objects and advantages of the present invention will become apparent from the following specication and appended drawings, in which Fig. l discloses a reflex klystron tube and its associated circuit according to the present invention; and

Fig. 2 is a graph illustrating the output of such a device.

Adjacent cathode I is a resonator 9 formed of a cylindrical outer shell I2, with an end plate It across one end of shell I2 and carrying a grid I4 centrally thereof. A reentrant pole I 0 is coaxial with shell I2 and carries a second grid `8 at its end adjacent to grid I4, thereby defining the resonator gap between the two grids. A ilexible diaphragm II is positioned across the other end of shell I2. fixed at its inner portion to pole I0.

Grids I4 and 8 may, as shown in Fig. 5 of the parent application, each consist of an annular member or ring provided with alternate long and short radial conducting bars, the rings being inserted in wall I3 and the end of pole I0. Concentric to grid I4 and close behind it is a reiiector electrode I8, which may be dish-shaped as shown.

Reflector I8 is supported by a rigid conductor I9 passing through the glass end bell 20, which, in

turn, is supported by and sealed to wall I3 ot resonator 9. Coaxial line terminal posts 2| and 22, which may be of the type shown in Fig. 4 oi the parent application, are provided having cou.-v

pling loops for extracting energy from the eld of the resonator 9. 'F

Fixed to the wall I2 of resonator 9 isa ange 29. A second flange 30 is fixed to pole I0. Tuning struts 6I are seated at one end in ange 30 and at the other end in screws 31 threadedly engaging flange 29, whereby, by rotation of screws 31, the separation of grids 8 and Illmay be adjusted to adjust the resonant frequency of the resonator.

Reentrant pole I0 of resonate1 9 continues beyond diaphragm II and flares out to form a flanged portion 60 parallel to flanges 29 and 30. Pole I0 is formed of one of the well-known alloys suitable for butt-sealing to certain glasses, and is sealed to a glass end bell `|52 having a. press 63 supporting the cathode structure I.

Grid 8 is maintained at a high positive potential relative to cathode I by means of battery 66, and reiiector I8 is maintained at or near the potential of cathode I by a lead 64 connected to a tap 13 of a potentiometer l5 connected across battery CB.

For the purpose of providing modulation of the output from resonator 8, as derived from terminal posts 2| or 22, lead 64 is also connected in series with the secondary 1i of a transformer 68 whose-primary 12 is supplied from the output of an amplifier 69 whose input microphone 1tor other suitable source of intelligence signal with which it is desired to modulate the oscillator. y

Fig. 2 shows the characteristics of the reflex kLvstron oscillator as a function of the voltage impressed upon the reflector plate. Curve 'i2l shows the relationship between the high frequency output intensity and the reflector plate voltage, while curve |22 shows the output frequency as a function of reflector plate voltage.

According to the present invention, the potential of the reflector electrode is varied in accordance with intelligence signals about a center value determined by the setting of potentiometer tap 1l, thereby suitably biasing the reflector electrode. For the purpose of producing frequency modulation, it will be seen that the region indicated between the vertical dotted lines is most useful, since in this region the amplitude of the l output remains substantially unchanged, while considerable variation in frequency can be encountered. It will be noted ,that in this region 1 the ultra-high-frequency output intensity or amplitude versus reflector voltage characteristic |23 has a substantially dat portion which coincides is controlled by a 4 positioned in the path of said stream for renecting the stream back into said resonator in the form of regularly-recurrent bunches whereby oscillations are produced, said apparatus having a frequency versus reflector voltage characteristic with a substantially linear portion, and means for maintaining the direct current potential of said reflecting electrode at substantially the center value oi' said linear portion of said characteristie, and means for varying the potential of said reflecting electrode in response to intelligence signals to effect-frequency modulation of the oscillations of said resonator by said signals;

2. High frequency modulator apparatus comprising a cavity resonator dimensioned to resonate at a selected frequency, means for projecting an electron stream through said resonator for effecting regularly-recurrent velocity changes in the `electron stream, means including a reflecting electrode for reflecting said stream back into said resonator in the form of regularlyrecurrent bunches to produce sustained oscillations within said resonator, said modulator apparatus having a frequency versus reilector voltage characteristic with a substantially linear portion, means for maintaining the direct current potential of said reilecting electrode at substantially the center value of said linear portion of said characteristic, a source of modulating signals having a, mean frequency different from said selected frequency, and means coupled to said reflecting electrode and said modulating signal source for varying the potential ofsaid electrode with the linear portion of the output frequency versus reflector voltage characteristic |22 with 1- respect to the reflector voltage. The reector plate voltage is therefore preferably varied between the values indicated by the vertical dotted lines of Fig.v 2, thereby producing a corresponding frequency variation between the horizontal dotted lines of the figure.

As will be observed, this portion of the frequency characteristic-is substantially linear for practical purposes, so that substantially linear frequency modulation can be produced. In view of the substantial flatness of the output intensity in the region between the dotted lines a variation in reflector voltage over this range will produce an amplitude-independent modulation of the output of the device.v A bias, such as that supplied by potentiometer 65, selected at the center value of the flat portion of the output intensity versus reflector voltage characteristic i23 corresponds to the center valuerof the linear portion of the output frequency versus reflector voltage curve |22. By modulating the reflector electrode I8 within the dotted line region amplitudein response to said signals substantially over said linear portion of said characteristic, whereby frequency modulation of said sustained oscillations is produced.

3. Apparatus as in claim 2 wherein said direct current potential maintaining mains and said reflector electrode potential varying means includes a transformer, said transformer having the secondary winding connected in series with said reflector electrode and the primary winding coupled to said modulating signal source.

independent modulation is produced. In this way, an extremely simple circuit is provided for usefully modulating the output of a reilex klystron. y

Since many changes could be made in the above construction and many apparently widely different embodiments of this .invention could be made without departing from the scope thereof. it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted 'as illustrative' and not in a limiting sense.

What is claimed is:

1. High frequency modulator apparatus comprising a cavity resonator, means -for projecting an electron stream through said resonator for effecting regularly-recurrent velocity changes in the electron stream, a reflecting electrode means iii) 4. Apparatus as in claim 2 wherein said direct current potential maintaining means includes a potentiometer and the secondary winding of a transformer, said winding of said transformer being connected between the center tap of said potentiometer and said reflector electrode.

5. High frequency modulator apparatus comprising a cavity resonator, means for projecting an electron streamk through said resonator for eecting regularly-recurrent velocity changes in the electrons of said stream, a reflector electrode positioned adjacent the point of exit of said stream from said resonator for reflecting the stream back into said resonator in the form of regularly-recurrent bunches, to produce sustained oscillations, said resonator having an ultra-high frequency intensity versus reflector y voltage characteristic with a substantially flat portion; andmeans for amplitude-independently modulating said oscillations including means for biasing said reflector electrode substantially 75 r'7.I Apparatus as in claim 5 wherein said reilector electrode biasing means and said reflector electrode potential varying means includes a transformer, said transformer having its secondary winding connected in series with said reflector electrode and its primary winding coupled to said modulating signal source.

8. High frequency modulator apparatus comprising a cavity resonator, means for projecti an electron stream through said resonator for effecting recurrent velocity changes in the electron stream, a reflecting electrode positioned in the path of said stream for reflecting the stream back into the resonator in the form of recurrent bunches whereby oscillations are produced in said resonator, a source of direct potential connected to said electrode, said apparatus having a frequency versus reflector voltage characteristie with a substantially linear portion, said apparatus further having a high frequency output amplitude versus reflector voltage characteristic also with a substantially linear portion and substantially coinciding with said rst linear portion with respect to said reiector voltage, said source of direct potential being adjustable for selecting substantially the center value of said linear portions, and a source of intelligence signal coupled to said electrode for varying the potential of said electrode within the substantially linear portions, whereby modulation of said oscillations by said intelligence signal is produced.

9. High frequency modulator apparatus comprising a cavity resonator, means for projecting an electron stream through said resonator for eifecting regularly-recurrent velocity changes in said electron stream, means including a reector electrode positioned in the path of said stream beyond said resonator for reflecting said stream back into said resonator in the form of regularlyrecurrent bunches whereby sustained oscillations are produced in said resonator, said apparatus having a frequency versus reflector voltage characteristic with a substantial linear portion, said apparatus further having an ultra high frequency output intensity versus reflector voltage characteristic with a substantially flat portion, said flat portion substantially coinciding with said linear portion with respect to said reflector voltage, means for biasing with a direct potential said vlreflector electrode at substantially the center value of said linear portion, and further means for applying a modulating signal to said reilector electrode within substantially said linear portion, whereby frequency modulation of said sustained oscillations is produced.

10. In an ultra-high frequency electron discharge device having a resonator, an electron source, means for forming an electron beam and projecting said beam through said resonator to effect regularly-recurrent velocity changes in said beam, a reflector electrode positioned in the path of said beam for reilecting said beam in the form of regularly-recurrent bunches back into said resonator to produce sustained oscillations therein, said device having a frequency versus reflector voltage characteristic with a substantially linear portion, the method of adjusting the bias of said reiiector electrode at substantially the center value of said linear portion.

11. The method as deiined in claim 10 further including the step of modulating the voltage of said reflector electrode within said linear portion.

EDWARD L. GINZTON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 22,506 Hahn June 27, 1944 y 2,281,935 Hansen et al May 5, 1942 2,406,850 Pierce Sept. 3, 1946 2,421,725 Stewart June 3, 1947 2,425,657 Tunick Aug. 12, 1947 2,434,704 Kroger Jan. 20, 1948 

